Gasoline engines emit undesirable amounts of hydrocarbon vapors when first started. This happens because liquid gasoline can become trapped in crevices in a cold engine and not be vaporized in time to participate in combustion and because the catalytic converter does not oxidize hydrocarbon vapors until it reaches a "light-off" temperature. This problem is exacerbated by the need to provide a fuel rich mixture when the engine is first started. One known way to reduce hydrocarbon emissions is to electrically heat part of the catalytic converter before starting the engine. This has the disadvantages of delaying starting and requiring large amounts of electrical energy at times when the battery is least able to supply such energy. Another known way to reduce hydrocarbon emissions at startup is to pass the exhaust through an adsorbent for storing hydrocarbon emissions. When the catalytic converter reaches operating temperature the adsorbent is flushed and the catalytic converter oxidizes the flushed hydrocarbons.
It is well known that a cold automobile engine fueled with methane exhausts less hydrocarbons than if fueled with gasoline. It is also well known that cold gasoline engines run more smoothly and efficiently if operated on methane instead of gasoline. Butanes and pentanes are less volatile than methane but offer similar advantages and are components of gasoline.
Canisters of activated carbon have been used for many years to adsorb fuel vapors produced while vehicles are not operating. The canisters are purged while the vehicle is operating thereby preparing them to adsorb fuel vapor again. A number of types of activated carbon are in current use or available made from raw materials such as wood and coal.
It is also well known that during purging activated carbon releases the most volatile fuel vapors first before releasing less volatile fuel vapors. Activated carbon charged with vapors from gasoline first releases predominantly butanes, then releases predominantly pentanes.
Oxygen sensors in the exhaust of gasoline engines have been standard equipment for many years. After a brief warmup period they indicate the presence of oxygen in the engine exhaust whereupon the information provided is used to optimize the delivery of fuel to the engine.
Current automobile engines include means for measuring or computing the amount of air entering the engine. This is most often accomplished by combining the rate of rotation of the engine, the displacement of the engine, the absolute pressure in the intake manifold and other factors according to an algorithm that provides the rate of flow of air into the engine. This is also accomplished by providing a hot wire anemometer or other mass flow sensor to directly measure the flow of air into the engine.
The velocity of sound in air is about 330 meters per second and the velocity of sound in butanes is about 215 meters per second. In a mixture the velocity varies between these values. In a stoichiometric mixture of air and butane the velocity of sound is about 15 meters per second slower than in pure air.
A general object of this invention is to provide a means for reducing hydrocarbon emissions and improving operation of gasoline powered engines during initial startup which also overcomes certain disadvantages of the prior art.